CT Dose Dependent on Multiphase Scanning, Protocol Choices

CT dosing is largely dependent on multiphase scanning and institutional protocols.

Multiphase scanning and institutional protocol choices are the primary factors that influence the considerable variation in CT doses within and across facilities, according to a study published in Radiology.

Researchers from the University of California (San Francisco, San Diego, and Irvine), and the Group Health Research Institute in Seattle, Washington, sought to determine patient, vendor, and institutional factors that influence CT radiation dose.

The researchers prospectively collected data on the volume CT dose index (CTDIvol) and effective dose in 274,124 head, chest, and abdominal CT examinations performed in adult patients at 12 facilities in 2013. They assessed patient, vendor, and institutional characteristics that could be used to predict median dose by using linear regression after log transformation of doses and high-dose examinations (top 25% of dose within anatomic strata).

The results showed a wide variation in dose within and across medical centers. For chest CTDIvol, overall median dose across all institutions was 11 mGy, and institutional median dose was 7–16 mGy. Models including patient, vendor, and institutional factors were good for prediction of median doses (R2 = 0.31–0.61). The specific institution where the examination was performed (reflecting the specific protocols used) accounted for a moderate to large proportion of dose variation. For chest CTDIvol, unadjusted median CTDIvol was 16.5 mGy at one institution and 6.7 mGy at another (adjusted relative median dose, 2.6 mGy).

The researchers noted several variables that were important predictors as to whether a patient would undergo high-dose CT. These included patient size, the specific institution where CT was performed, and the use of multiphase scanning. “For example, while 49 percent of patients (21,411 of 43.696) who underwent multiphase abdominal CT had a high-dose examination, 8 percent of patients (4,977 of 62,212) who underwent single-phase CT had a high-dose examination. If all patients had been examined with single-phase CT, 69 percent (18,208 of 26,388) of high-dose examinations would have been eliminated,” they wrote. Patient size, institutional-specific protocols, and multiphase scanning were the most important predictors of dose, followed by manufacturer, and iterative reconstruction.

The researchers concluded that CT doses varied considerably within and across facilities primary factors influencing dose variation being multiphase scanning and institutional protocol choices. It is unknown if the variation in these factors influenced diagnostic accuracy.